1. Field of the Invention
The present invention relates to a semiconductor device and a process to form the semiconductor device. In particular, the invention relates to a semiconductor device including an active device made of nitride based compound semiconductor material, and a substrate made of silicon (Si).
2. Related Background Art
One type of semiconductor devices has been well known as, what is called, a monolithic microwave integrated circuit (hereafter denoted as MMIC). Eli Reese et al. have disclosed one of such MMICs in the digest of IEEE International Microwave Symposium 2010, pp. 1230 to 1233. The MMIC disclosed therein has an arrangement of the substrate made of silicon carbide (SiC) and a gallium nitride (GaN) layer epitaxially grown on the SiC substrate. Such an MMIC with the SiC substrate inherently shows excellent heat dissipation and high frequency performance.
However, available SiC substrates are generally cost ineffective, which inevitably raises the market price of the MMIC applying the SiC substrate. Another material for the substrate has been investigated. In particular, a substrate made of silicon (Si) has various advantages when it is applied to the MMIC except that Si has the thermal conductivity less than that of SiC. Accordingly, additional or especial arrangement to dissipate heat from the active device made of nitride based material is necessary to use Si substrate for the MMIC.